[Paper Review] The ESO UVES Advanced Data Products Quasar Sample - I. Dataset and New N_HI Measurements of Damped Absorbers

Tayyaba Zafar, Attila Popping+1 more|arXiv (Cornell University)|Jul 2, 2013

Astrophysics and Star Formation StudiesPhysics and Astronomy53 references21 citations

TL;DR

This paper presents a high-resolution quasar absorption line dataset from the ESO UVES Advanced Data Products archive, comprising 250 spectra with redshifts up to z = 6.311. It reports new H i column density measurements for 19 damped and sub-damped Lyα absorbers (DLAs/sub-DLAs), including 10 new identifications and 19 first-time measurements, confirmed via Voigt profile fitting and detection of metal or Lyman-series lines.

ABSTRACT

We present here a dataset of quasars observed with the Ultraviolet Visual Echelle Spectrograph (UVES) on the VLT and available in the ESO UVES Advanced Data Products archive. The sample is made up of a total of 250 high resolution quasar spectra with emission redshifts ranging from 0.191 < z_em <6.311. The total UVES exposure time of this dataset is 1560 hours. Thanks to the high resolution of UVES spectra, it is possible to unambiguously measure the column density of absorbers with damping wings, down to N_HI > 10^{19} cm^{-2}, which constitutes the sub-damped Lya absorber (sub-DLA) threshold. Within the wavelength coverage of our UVES data, we find 150 damped Lya systems (DLAs)/sub-DLAs in the range 1.5 < z_abs < 4.7. Of these 150, 93 are DLAs and 57 are sub-DLAs. An extensive search in the literature indicates that 6 of these DLAs and 13 of these sub-DLAs have their N_HI measured for the first time. Among them, 10 are new identifications as DLAs/sub-DLAs. For each of these systems, we obtain an accurate measurement of the HI column density and the absorber's redshift in the range 1.7 < z_abs < 4.2 by implementing a Voigt profile-fitting algorithm. These absorbers are further confirmed thanks to the detection of associated metal lines and/or lines from members of the Lyman series. In our data, a few quasars' lines-of-sight are rich. An interesting example is towards QSO J0133+0400 (z_em = 4.154) with six DLAs and sub-DLAs reported.

Motivation & Objective

• To compile a comprehensive dataset of high-resolution quasar spectra from the ESO UVES Advanced Data Products archive for studying neutral hydrogen absorbers.
• To identify and measure H i column densities for damped Lyα absorbers (DLAs) and sub-damped Lyα absorbers (sub-DLAs) in the redshift range 1.5 < z < 4.7.
• To detect and characterize previously unreported DLAs and sub-DLAs, particularly those below the traditional DLA threshold (N_HI ≥ 2×10²⁰ cm⁻²), to improve understanding of cosmic gas mass and metallicity evolution.
• To confirm new absorbers through detection of associated metal lines and higher-order Lyman series transitions.
• To provide a foundation for future statistical studies of DLA/sub-DLA properties, including column density distributions and contributions to gas mass density.

Proposed method

• Utilized high-resolution UVES spectra (R ~ 40,000) from the ESO UVES Advanced Data Products archive, covering wavelengths from 300 to 1100 nm.
• Applied automated and visual searches to identify damped Lyα absorbers (DLAs) and sub-DLAs based on damping wings in the Lyα profile.
• Performed Voigt profile fitting to the Lyα line and higher-order Lyman series transitions (e.g., Lyβ, Lyγ) to derive accurate H i column densities (N_HI).
• Confirmed absorber identifications by detecting associated metal lines (e.g., C II, Si II, Zn II) and higher Lyman-series lines in the UV coverage.
• Classified systems as DLAs (N_HI ≥ 2×10²⁰ cm⁻²) or sub-DLAs (10¹⁹ ≤ N_HI < 2×10²⁰ cm⁻²) based on measured column densities.
• Used a consistent redshift and column density measurement pipeline across all 250 quasar spectra to ensure homogeneity and reproducibility.

Experimental results

Research questions

• RQ1 What is the distribution of H i column densities for damped and sub-damped Lyα absorbers in a high-resolution quasar sample from the UVES archive?
• RQ2 How many new damped absorbers (DLAs/sub-DLAs) are identified in this dataset, and how many have their H i column densities measured for the first time?
• RQ3 Which lines-of-sight contain multiple absorbers, and what is the kinematic structure of these complex systems?
• RQ4 To what extent do metal lines and higher Lyman-series transitions confirm the presence of new absorbers in the sample?
• RQ5 How do the column density distributions of DLAs and sub-DLAs in this sample compare to previous studies, particularly in terms of sub-DLA contributions to gas mass density?

Key findings

• The dataset comprises 250 high-resolution quasar spectra with emission redshifts ranging from z_em = 0.191 to z_em = 6.311, totaling 1560 hours of UVES exposure time.
• A total of 150 damped and sub-damped Lyα absorbers were identified in the redshift range 1.5 < z_abs < 4.7, with 93 classified as DLAs and 57 as sub-DLAs.
• Among these, 6 DLAs and 13 sub-DLAs have their H i column densities measured for the first time, including 10 new absorber identifications.
• The H i column densities were measured with high accuracy using Voigt profile fitting to the Lyα line and higher Lyman-series transitions where available.
• The line-of-sight toward QSO J0133+0400 contains six DLAs and sub-DLAs, including two sub-DLAs at z = 3.995 and z = 3.999 separated by only 240 km s⁻¹, indicating a dense absorber system.
• Five proximate DLA cases and four quasar pairs were identified, with differential absorption detected in some pairs, such as QSO B0307-195B hosting a sub-DLA at z = 1.788 while its companion does not.